There has long been a need for a drug release system which is soft, pliable and elastic, oxygen and water vapor permeable, translucent, yet high in tensile strength and abrasion resistance, biocompatible and which can release a wide variety of drugs in a controlled, sustained manner.
A drug release system or medical patch can be a transdermal patch or transdermal drug release system for use on intact skin for therapeutic effects not necessarily in the area on which such a system is applied. An example is the release of Nitroglycerine from such a release system applied on the skin of the chest for the treatment of Angina Pectoris.
A drug release system or medical patch may also be a wound dressing for delivery of drugs to a specific site to topically treat a local wound. Sustained release of drugs directly to a wound site provides long lasting therapeutic action without the danger of toxic side effects that can occur with systemic drug delivery (by injection or capsule). Systemic antibiotics, for example, must be administered within four hours of wounding, when circulation is still optimal. If treatment is delayed, conditions for bacterial growth will develop, and complete curing would be more difficult. Once an infection is established, it becomes difficult to systemically administer certain antibiotics for extended periods at levels that are safe, yet still effective at the wound site. Drugs administered systemically, rather than applied locally, are distributed throughout the body; thus, the amount of drugs actually reaching the target is only a small part of the total dosage. This problem is further compounded in the trauma patient by shock, which decreases vascular flow to the tissue.
In addition, a drug release system or medical patch can be used for prosthetic devices within the body. If used as a prosthetic device, the most significant criteria for the material is that it be biocompatible. That is, the material should not induce the formation of a thrombus which can embolize into the peripheral bloodstream.
Although there are now on the market dressing "skin patches" that contain a few specific drugs such as nitroglycerine and scopolamine, a system is needed which can deliver many drugs never before encapsulated in a patch. Since most drug compounds are highly sensitive to environmental influences, they can be chemically damaged by a thermal curing process or organic solvents.
At present, the most commercially successful burn and superficial skin wound dressing is a polyether-based polyurethane, moisture-vapor permeable membrane compounded with silica gel. The composition, known as "Op-Site".RTM., described in U.S. Pat. Nos. 4,340,043 and 4,460,369 assigned to Smith & Nephew Ltd., is in the form of a thin film having a surface coated with a polyvinylethylether adhesive. This material, however, still suffers from the inability to incorporate biologically active agents such as coagulants and antibiotics into the membrane, rather than into the adhesive, and from difficulty in formation and application as a bandage which conforms to the contour of the site of application.
It has now been discovered that the variety of drugs which can be incorporated into the medical patch can be widened by the use of a specific light-cured rather than heat-cured polyurethane in the drug releasing layer or member as a matrix for a therapeutically effective amount of drug dispersed therein.